Invertase biosynthesis by Saccharomyces carlsbergensis in batch and continuous cultures

Production of biomass and beta-D-galactosidase by Candida pseudotropicalis grown in continuous culture on whey

The production of biomass and beta-D-galactosidase by the lactose-utilizing yeast Candida pseudotropicalis NCYC 744 in whey medium was studied. Apparent optimization of growth conditions and medium was done in continuous culture. Optimal pH and temperature were 2.6 and 36-38 degrees C, respectively, Limitations in Cu, Zn, and possibly Mn were detected in deproteinized whey medium. Additions of tryptophan stimulated growth of the yeast. Under optimal conditions in medium supplemented with excess tryptophan, Cu, Zn, and Mn the maximum values obtained: yeast concentration, 4.6 g/L; yeast productivity, 1.4 g/L h (at D = 0.35 h(-1)); enzyme volumetric productivity, 2100 U/L h (at D = 0.25 h(-1)); maintenance coefficient, 5-10 mg lactose/g cell h; saturation constant (K(s)) for lactose, 4.76mM; maximum specific growth rate, (mu(max)), 0.47 h(-1). No significant increase in specific enzyme activity (U/mg cell) was observed after medium optimization evidencing the importance of regulatory controls in enzyme synthesis.

Theoretical and methodological studies of continuous microbial bioreactors

This article reviews most of the author's studies on process development and reactor design for continuous microbial reactions. (1) Enzyme reactions of growing and non-growing microbial cells immobilized in agar gel beads were analyzed pertaining to the effects of external and internal diffusion of substrate on reaction kinetics. (2) Experimental correlations of production rates of beta-fructosidase and acid phosphatase with dilution rate of continuous culture were simulated based on an operon model for enzyme regulation. (3) Population dynamics of an amylase-producing bacteria and their mutant were discussed in relation to enzyme productivity in a continuous culture of spore-forming bacteria. (4) Plasmid mobilization in a mixed population of donor, recipient, and helper cells was investigated in a continuous culture as a model study of accidental release of a genetically modified plasmid into a natural environment. (5) A production rate increase of up to 100-fold was achieved by cell-recycle culturing of continuous acetic acid fermentation using a filter module with a hollow fiber membrane. (6) The feasibility of a continuous surface culture for the biooxidation of organic substances was ascribed to an enhanced oxygen absorption rate in the presence of a microbial film on a liquid surface. (7) Simultaneous separation of inhibitory products using an electrodialysis module during some organic acid fermentations was effective for increasing production in a continuous culture.

Production of Maltase by Wild-Type and a Constitutive Mutant of Saccharomyces italicus

The production of maltase, an inducible and repressible catabolic enzyme in Saccharomyces italicus , was studied and compared in batch, fed-batch, and continuous fermentations. Tight genetic controls on maltase synthesis limited the effect of environmental manipulations such as fed-batch or continuous culture in enhancement of maltase synthesis, and neither approach was able to improve the performance above the batch process for maltase production. S. italicus was mutated, and a constitutive producer of maltase was isolated. The mutant was detected by its ability to grow on sucrose, which is a noninducing substrate that is hydrolyzed by maltase; S. italicus does not possess invertase and will not normally grow on sucrose. Maltase production by this mutant was studied during growth on sucrose in batch and continuous cultures and marked improvement in enzyme productivity was observed. The specific activity of maltase produced by this mutant was more than twice that of the parent wild type: 2,210 and 1,370 U/g of cells for the mutant versus 890 and 510 U/g of cells for the wild type in batch and continuous cultures, respectively. Maltase specific productivity was increased from 74 to 288 U/g of cells per h by switching from batch growth of the wild type to continuous cultivation of the mutant.

Mathematical model of cell growth and phosphatase biosynthesis in Saccharomyces carlsbergensis under phosphate limitation

The rate kinetics of growth and acid phosphate formation in the batch culture of Saccharomyces carlsbergensis LAM 1068 was studied under varying degrees of phosphate limitation. The mathematical model that was developed is concerned with the time lag for exponential growth, the biphasic growth on a substrate (glucose) and its product (ethanol), sustained growth on conservative phosphate, and the derepression of acid phosphatase. The numerical calculations using appropriate parametric constants successfully described the variation in the cell mass, glucose, ethanol, and inorganic phosphate concentrations, and the enzyme activity of acid phosphatase during aerobic growth of S. carlsbergensis under five different conditions of phosphate starvation. A simulation study revealed that the optimum initial phosphate concentration in the medium giving a high productivity of acid phosphatase was 2.0 mg phosphorus/g glucose liter.

Modeling the role of cyclic AMP in catabolite repression of inducible enzyme biosynthesis in microbial cells

Modeling the role of cyclic AMP (cAMP) in catabolite repression of inducible enzyme production in microbial cells was studied. A catabolite repression index, F, was defined based on the postulation that complex formation occurs between RNA polymerase (RNAP) and DNA, and shifting from the inert form to the open form of this complex (the latter form is required for transcription) is accelerated by the cAMP.CRP complex. The catabolite repression index, F, was incorporated into model equations of mRNA production. Empirical relationships between intracellular cAMP level and medium glucose concentration were established based on experimental data and introduced into the model. Computer simulation results were obtained for a number of interesting cases. The practical utility of the proposed model was demonstrated by comparing it with the experimental results on glucose isomerase biosynthesis.

Genetic control of invertase formation in Saccharomyces cerevisiae. II. Isolation and characterization of mutants conferring invertase hyperproduction in strain EK-6B carrying the SUC3 gene

Invertase formation in the yeast Saccharomyces cerevisiae is subject to repression by hexoses in the growth medium. Mutagen-induced (ethyl methanesulfonate or N-methyl-N-nitro-nitrosoguanidine) invertase hyperproducer mutants have been derived from the SUC3 MAL3 strain EK-6B by selecting for their ability to grow on media containing the sugar raffinose plus 2-deoxy-D-glucose (2DG). Raffinose like sucrose is a betta-fructoside which can be hydrolyzed by yeast invertase (beta-fructoside which can be hydrolyzed by yeast invertase (beta-fructofuranoside fructohydrolase). These mutants, designated dgr, produce higher levels of invertase (pi-glucosidase levels are also elevated but to a lesser extent) under conditions normally repressing invertase biosynthesis in the parent. Invertases of mutants dgr2 and dgr3 are indistinguishable from that of EK-6B with respect to their Km's for sucrose and thermal labilities. Genetic studies revealed that dgr2 and dgr3 are recessive and unlinked to the SUC3 gene.

Dual control of invertase biosynthesis in chemostat culture

In a previous study on the chemostat culture of Saccharomyces carlsbergensis, maximum invertase specific activity was observed at an intermediate dilution rate. A possible regulation mechanism, assuming there are simultaneous effects of induction and repression on two sites of the operator loci for invertase formation, is proposed which might account for the observed curve of the dilution rate effect.